1 Answer

This question is a little vague, so I'm going to have to make some assumptions.

This is in Sun/Moon, meaning that the Riolu is being encountered at level 52.

You are using a standard Poké Ball.

Riolu is not affected by a status condition.

Riolu is at 2% of its HP.

Using the Catch Rate Calculator for Gen VI (although the standard Poké Ball catch rate is unchanged in Gen VII), a Riolu under these conditions has a catch rate of 39.577%.
With False Swipe your odds rise a tiny bit, up to 39.758%.

If you Paralyze this Riolu, the catch rate rises to 53.644%.
With False Swipe, it rises to 53.885%.